Products and members with a resin film on their surface are used in a wide range of applications. They are used as fabricated and/or endowed with a function as appropriate to the intended use. In the nature of resin, such products and members generally have a hydrophobic or lipophilic surface. If stains such as oily stains adhere to their hydrophobic or lipophilic surface, they are hard to remove. If accumulated, stains can significantly impair the functions or characteristics of the products and members. Where exposed to rain or high humidity, the hydrophobic or lipophilic surface will have water droplets thereon to cause irregular reflection, which damages transmission of transparent products and members. Even products and members with an inorganic surface, such as glass and metals, cannot be seen as sufficient in resistance against adhesion of oily stains and against fogging due to adhesion of water droplets. Automotive glass and architectural glass often fails to provide an unobstructed, clear, transmitted view (or reflected view in the case of mirrors) as a result of adhesion of hydrophobic contaminants, such as urban dust, combustion products (e.g., carbon black contained in exhaust gases from automobiles), fats and oils, and substances released from some sealant materials, or water droplets. Therefore, imparting such functions as anti stain properties and anti fog properties to glass particularly in the applications described has keenly be demanded.
Assuming that stains are organic substances such as oils, achieving anti stain properties requires reducing the interaction between the stains and the surface to be protected from stains by making the surface hydrophilic or oil-repellent. Imparting anti fog properties requires making the surface spreading-wettable (capable of evenly spreading adhered water droplets, namely, hydrophilic) or water-repellent (helping remove adhered water droplets). Hence, many of anti-stain/fog materials under current studies rely for the anti stain/fog properties on surface treatment for imparting hydrophilicity, water repellency or oil repellency.
Conventionally proposed hydrophilizing surface treatments, such as an etching treatment and a plasma treatment, achieve a high hydrophilization degree, but the effect is temporary, and the hydrophilized state does not last long. The Chemical Daily, in a Jan. 30, 1995 article, reports a surface hydrophilic coat of a hydrophilic graft polymer, which is among hydrophilic resins. According to the report, the coat exhibits hydrophilicity to some extent but cannot be seen as having sufficient affinity to a substrate, still requiring improvement in durability.
Other known members with surface hydrophilicity include those utilizing titanium oxide as a photocatalyst. The hydrophilization by a photocatalyst is based on the functions of a photocatalyst for oxidatively decomposing and hydrophilizing organic matter which are developed on exposure to light. For instance, WO96/29375 discloses a hydrophilizing method, in which a photocatalyst layer is formed on a substrate and photoexcited to make the surface of the substrate highly hydrophilic. WO96/29375 says that the method is applicable to glass, lenses, mirrors, exterior materials, water-related products, and so forth to provide composite materials with high resistance to fogging and staining. Glass members having a titanium oxide coat have been used as self-cleaning architectural or automotive window glass. However, prolonged exposure to sunlight is necessary before the self-cleaning material manifests the anti stain/fog functions. The anti stain/fog properties are unavoidably deteriorated as dirt is accumulated with time. The coating film strength per se cannot be regarded as sufficient, leaving room for improvement on durability. Self-cleaning film having a plastic substrate coated with a titanium oxide layer is used as automotive side mirrors, etc. Neither is it regarded as having sufficient film strength, and a hydrophilic material with superior wear resistance has been sought for.
On the other hand, anti stain/fog materials that have most been used to produce water or oil repellency include silicone compounds and fluorine compounds. For example, JP-A 4-338901 discloses an anti stain material having a substrate coated with a silanol-terminated orqanopolysiloxane; JP-B 6-29332 proposes a material having a silane compound containing a polyfluoroalkyl group; and JP-A 7-16940 teaches a combination of a silicon dioxide-based optical thin film and a copolymer of a perfluoroacrylate and a monomer having an alkoxysilane group. Nevertheless anti stain materials of these types have insufficient anti stain properties and are hardly cleared of such stains like fingerprints, sebum, sweat, and cosmetics. Additionally, a surface treatment with a low surface energy compound such as a fluorine or silicone compound is seen as reducing in function with time. Development of anti stain/fog members with high durability has therefore been eagerly demanded.